Reproducing apparatus capable of reproducing picture data

ABSTRACT

A reproducing apparatus includes a graphics processing unit that outputs graphics data, which forms a first screen image, in sync with a vertical sync signal and a pixel clock signal, a video decoder that outputs video data, which forms a second screen image, in sync with the vertical sync signal and the pixel clock signal, a blending process unit that executes a blending process for blending the graphics data, which is output from the graphics processing unit, and the video data, which is output from the video decoder, and a picture data output unit that outputs picture data, which is obtained by the blending process, to a display apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-000248, filed Jan. 4, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reproducing apparatus such as a highdefinition digital versatile disc (HD-DVD) player.

2. Description of the Related Art

In recent years, with a progress in digital compression-encodingtechnology for motion video, reproducing apparatuses (players), whichcan handle high-definition video according to the high definition (HD)standard, have steadily been developed.

In this type of player, there is a demand for blending video data andgraphics data at a high level, thereby to enhance interactivity. Alphablending is known as a technique for blending picture data. The alphablending is a blending technique wherein alpha data, which representsthe degree of transparency of each pixel of a picture, is used tooverlay this picture on another picture.

Japanese Patent Application KOKAI Publication No. 8-205092, forinstance, discloses a system in which graphics data and video data aremixed by a display controller. In that system, the display controllercaptures video data and overlays the captured video data on a partialarea of a graphics screen.

The system of Japanese Patent Application KOKAI Publication No.8-205092, however, presupposes that video data with a relatively lowresolution is handled. In that system, no consideration is given to thehandling of high-definition pictures such as HD-standard video data. Theamount of HD-standard video data, which is to be processed per unittime, is enormous, and it is practically difficult for the displaycontroller to capture HD-standard video data.

It is thus desirable to realize a system architecture wherein videodata, which is output from, e.g., a video decoder, and graphics data,which is output from a display controller, are blended not within thedisplay controller, but by an external blending circuit.

However, in usual cases, video data output from the video decoder andgraphics data output from the display controller are asynchronous. It isthus necessary to provide within the blending circuit a buffer fortemporarily storing video data or graphics data. This makes thestructure of the blending circuit very complex.

Under the circumstances, there is a demand for the advent of areproducing apparatus that can efficiently execute blending of videodata and graphics data with a simple structure.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided areproducing apparatus comprising a graphics processing unit that outputsgraphics data, which forms a first screen image, in sync with a verticalsync signal and a pixel clock signal; a video decoder that outputs videodata, which forms a second screen image, in sync with the vertical syncsignal and the pixel clock signal; a blending process unit that executesa blending process for blending the graphics data, which is output fromthe graphics processing unit, and the video data, which is output fromthe video decoder; and a picture data output unit that outputs picturedata, which is obtained by the blending process, to a display apparatus.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a block diagram that shows the structure of a reproducingapparatus according to an embodiment of the present invention;

FIG. 2 shows the structure of a player application that is used in thereproducing apparatus shown in FIG. 1;

FIG. 3 is a view for explaining the functional structure of a softwaredecoder that is realized by the player application shown in FIG. 2;

FIG. 4 is a view for explaining a blending process that is executed by ablending process unit, which is provided in the reproducing apparatusshown in FIG. 1;

FIG. 5 is a view for explaining a blending process that is executed by aGPC, which is provided in the reproducing apparatus shown in FIG. 1;

FIG. 6 shows a state in which sub-video data is overlaid on main videodata in the reproducing apparatus shown in FIG. 1;

FIG. 7 shows a state in which main video data is displayed on a partialarea of sub-video data in the reproducing apparatus shown in FIG. 1;

FIG. 8 illustrates an operation in which main video data and graphicsdata are transferred to the blending process unit in the reproducingapparatus shown in FIG. 1;

FIG. 9 illustrates a state in which graphics data and alpha data aretransferred in synchronism in the reproducing apparatus shown in FIG. 1;

FIG. 10 illustrates a state in which graphics data and alpha data aretransferred over different transmission lines in the reproducingapparatus shown in FIG. 1;

FIG. 11 is a block diagram that shows a first example of the structureof the blending process unit that is provided in the reproducingapparatus shown in FIG. 1;

FIG. 12 is a block diagram that shows a second example of the structureof the blending process unit that is provided in the reproducingapparatus shown in FIG. 1;

FIG. 13 is a block diagram that shows a third example of the structureof the blending process unit that is provided in the reproducingapparatus shown in FIG. 1;

FIG. 14 is a block diagram that shows a fourth example of the structureof the blending process unit that is provided in the reproducingapparatus shown in FIG. 1;

FIG. 15 is a view for explaining color conversion and an α arithmeticoperation, which are executed by the blending process unit provided inthe reproducing apparatus shown in FIG. 1;

FIG. 16 is a block diagram that shows a fifth example of the structureof the blending process unit that is provided in the reproducingapparatus shown in FIG. 1;

FIG. 17 is a block diagram that shows a sixth example of the structureof the blending process unit that is provided in the reproducingapparatus shown in FIG. 1; and

FIG. 18 is a block diagram that shows a seventh example of the structureof the blending process unit that is provided in the reproducingapparatus shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings.

FIG. 1 shows an example of the structure of a reproducing apparatusaccording to an embodiment of the present invention. The reproducingapparatus is a media player that reproduces audio/video (AV) content.The reproducing apparatus is realized as an HD-DVD player thatreproduces audio/video (AV) content, which is stored on DVD mediaaccording to HD-DVD (High Definition Digital Versatile Disc) standard.

As is shown in FIG. 1, the HD-DVD player includes a central processingunit (CPU) 11, a north bridge 12, a main memory 13, a south bridge 14, anonvolatile memory 15, an audio codec 16, a universal serial bus (USB)controller 17, an HD-DVD drive 18, an audio bus 19, a graphics bus 20, aperipheral component interconnect (PCI) bus 21, a video controller 22,an audio controller 23, an audio decoder 24, a video decoder 25, ablending process unit 30, audio mixers 31, 32, a video encoder 40, andan AV interface (HDMI-TX) 41 such as a high definition multimediainterface (HDMI).

In this HD-DVD player, a player application 150 and an operating system(OS) 151 are preinstalled in the nonvolatile memory 15. The playerapplication 150 is software that runs on the OS 151, and executes acontrol to reproduce AV content that is read out of the HD-DVD drive 18.

AV content, which is stored on HD-DVD media, which is driven by theHD-DVD drive 18, contains a motion video stream (HD-DVD stream) such asa stream that is compression-encoded by H.264 or MPEG2 format. In theHD-DVD stream, compression-encoded main video data (motion video),compression-encoded main audio data, compression-encoded graphics dataincluding alpha data, and compression-encoded sub-audio data aremultiplexed.

The compression-encoded main video data is data that is obtained byencoding motion video data, which is used as main video (main screenpicture), according to the H.264/AVC encoding scheme. The main videodata contains an HD standard high-definition picture. Alternatively,main video data according to standard definition (SD) scheme can beused. The compression-encoded graphics data is sub-video (sub-screenpicture) that is displayed in a state in which the sub-video is overlaidon main video. The graphics data contains sub-video data, which isformed of motion video that supplements the main video, sub-picture dataincluding text (e.g., caption)/still picture, and navigation data(Advanced Navigation) for displaying operation guidance such as a menuobject. The navigation data contains still picture/motion video(including animation)/text. The navigation data includes a script inwhich the motion of an object picture such as a menu object isdescribed. The script is interpreted and executed by the CPU 11.Thereby, a menu object with high interactivity can be displayed on mainvideo.

These sub-video data, sub-picture data and navigation data arecompression-encoded.

The HD-standard main video has a resolution of, e.g., 1920×1080 pixelsor 1280×720 pixels. Each of the sub-video data, sub-picture data andnavigation data has a resolution of, e.g., 720×480 pixels.

In this HD-DVD player, software (player application 150) executes aseparation process for separating main video data, main audio data,graphics data and sub-audio data from a HD-DVD stream that is read outfrom the HD-DVD drive 18, and a decoding process for decoding thegraphics data and sub-audio data. On the other hand, dedicated hardwareexecutes a decoding process for decoding main video data and main audiodata, which typically use a greater amount of processing.

The CPU 11 is a processor that is provided in order to control theoperation of the HD-DVD player. The CPU 11 executes the OS 151 andplayer application 150, which are loaded from the nonvolatile memory 15into the main memory 13. In one embodiment, a part of the memory areawithin the main memory 13 is used as a video memory (VRAM) 131. It isnot necessary, however, to use a part of the memory area within the mainmemory 13 as the VRAM 131. The VRAM 131 can be provided as a memorydevice that is independent from the main memory 13.

The north bridge 12 is a bridge device that connects a local bus of theCPU 11 and the south bridge 14. The north bridge 12 includes a memorycontroller that access-controls the main memory 13. The north bridge 12also includes a graphics processing unit (GPU) 120.

The GPU 120 is a graphics controller that generates graphics data (alsoreferred to as graphics picture data), which forms a graphics screenpicture, from data that is written by the CPU 11 in the video memory(VRAM) 131 that is assigned to the partial memory area of the mainmemory 13. The GPU 120 generates graphics data using a graphicsarithmetic function such as bit block transfer. For example, in a casewhere picture data (sub-video, sub-picture, navigation) are written inthree planes in the VRAM 131 by the CPU 11, the GPU 120 executes ablending process, with use of bit block transfer, which blends thepicture data corresponding to the three planes on a pixel-by-pixelbasis, thereby generating graphics data for forming a graphics screenpicture with the same resolution (e.g., 1920×1080 pixels) as the mainvideo. The blending process is executed using alpha data that areassociated with the picture data of sub-video, sub-picture andnavigation, respectively. The alpha data is a coefficient representativeof the degree of transparency (or non-transparency) of each pixel of theassociated picture data. The alpha data corresponding to the sub-video,sub-picture and navigation are multiplexed on the stream along with thepicture data of the sub-video, sub-picture and navigation. Specifically,each of the sub-video, sub-picture and navigation included in the streamcontains picture data and alpha data.

The graphics data that is generated by the GPU 120 has an RGB colorspace. Each pixel of the graphics data is expressed by digital RGB data(24 bits).

The GPU 120 includes not only the function of generating graphics datathat forms a graphics screen picture, but also a function of outputtingalpha data, which corresponds to the generated graphics data, to theoutside.

Specifically, the GPU 120 outputs the generated graphics data to theoutside as an RGB video signal, and outputs the alpha data, whichcorresponds to the generated graphics data, to the outside. The alphadata is a coefficient (8 bits) representative of the transparency (ornon-transparency) of each pixel of the generated graphics data (RGB).The GPU 120 outputs, on a pixel-by-pixel basis, alpha-data-addedgraphics data (32-bit RGBA data), which contains graphics data (24-bitdigital RGB video signal) and alpha data (8-bit). The alpha-data-addedgraphics data (32-bit RGBA data) is sent to the blending process unit 30in sync with each pixel over the dedicated graphics bus 20. The graphicsbus 20 is a transmission line that is connected between the GPU 120 andthe blending process unit 30.

In this HD-DVD player, the alpha-data-added graphics data is directlysent from the GPU 120 to the blending process unit 30 via the graphicsbus 20. Thus, there is no need to transfer the alpha data from the VRAM131 to the blending process unit 30 via, e.g., the PCI bus 21, and it ispossible to avoid an increase in traffic of the PCI bus 21 due to thetransfer of alpha data.

If the alpha data were to be transferred from the VRAM 131 to theblending process unit 30 via, e.g., the PCI bus 21, it would typicallybe necessary to synchronize the graphic data output from the GPU 120 andthe alpha data transferred via the PCI bus 21 within the blendingprocess unit 30. This leads to complexity in structure of the blendingprocess unit 30. In this HD-DVD player, the GPU 120 outputs the graphicsdata and alpha data by synchronizing them on a pixel-by-pixel basis.Therefore, synchronization between the graphics data and alpha data caneasily be realized.

The south bridge 14 controls the devices on the PCI bus 21. The southbridge 14 includes an IDE (Integrated Drive Electronics) controller forcontrolling the HD-DVD drive 18. The south bridge 14 has a function ofaccessing the nonvolatile memory 15, USB controller 17 and audio codec16.

The HD-DVD drive 18 is a drive unit for driving storage media such asHD-DVD media that stores audio/video (AV) content according to theHD-DVD standard.

The audio codec 16 converts software-decoded sub-audio data to an I2S(Inter-IC Sound) format digital audio signal. The audio codec 16 isconnected to the audio mixers (Audio Mix) 31 and 32 via the audio bus19. The audio bus 19 is a transmission line that is connected betweenthe audio codec 16 and the audio mixers (Audio Mix) 31 and 32. The audiobus 19 transfers the digital audio signal from the audio codec 16 to theaudio mixers (Audio Mix) 31 and 32, not through the PCI bus 21.

The video controller 22 is connected to the PCI bus 21. The videocontroller 22 is an LSI for executing interface with the video decoder25. A stream (Video Stream) of main video data, which is separated fromthe HD-DVD stream by software, is sent to the video decoder 25 via thePCI bus 21 and video controller 22. In addition, decode controlinformation (Control) that is output from the CPU 11 is sent to thevideo decoder 25 via the PCI bus 21 and video controller 22.

In one embodiment, the video decoder 25 is a decoder that supports theH.264/AVC standard. The video decoder 25 decodes HD-standard main videodata and generates a digital YUV video signal that forms a video screenpicture with a resolution of, e.g., 1920×1080 pixels. The digital YUVvideo signal is sent to the blending process unit 30.

The audio controller 23 is connected to the PCI bus 21. The audiocontroller 23 is an LSI for executing interface with the audio decoder24. A stream (Audio Stream) of main video data, which is separated fromthe HD-DVD stream by software, is sent to the audio decoder 24 via thePCI bus 21 and audio controller 23.

The audio decoder 24 decodes the main audio data and generates an I2S(Inter-IC Sound) format digital audio signal. This digital audio signalis sent to the audio mixers (Audio Mix) 31 and 32 via the audiocontroller 23.

The blending process unit 30 is connected to the GPU 120 and videodecoder 25, and executes a blending process for blending graphics data,which is output from the GPU 120, and main video data, which is decodedby the video decoder 25. Specifically, this blending process is ablending process (alpha blending process) for blending, on apixel-by-pixel basis, the digital RGB video signal, which forms thegraphics data, and the digital YUV video signal, which forms the mainvideo data, on the basis of the alpha data that is output along with thegraphics data (RGB) from the GPU 120. In this case, the main video datais used as a lower-side screen picture, and the graphics data is used asan upper-side screen picture that is overlaid on the main video data.

The output picture data that is obtained by the blending process isdelivered, for example, as a digital YUV video signal, to the videoencoder 40 and AV interface (HDMI-TX) 41. The video encoder 40 convertsthe output picture data (digital YUV video signal), which is obtained bythe blending process, to a component video signal or an S-video signal,and outputs it to an external display device (monitor) such as a TVreceiver. The AV interface (HDMI-TX) 41 outputs digital signalsincluding the digital YUV video signal and digital audio signal to anexternal HDMI device.

The audio mixer (Audio Mix) 31 mixes the sub-audio data, which isdecoded by the audio codec 16, and the main audio data, which is decodedby the audio decoder 24, and outputs the mixed result as a stereo audiosignal. The audio mixer (Audio Mix) 32 mixes the sub-audio data, whichis decoded by the audio codec 16, and the main audio data, which isdecoded by the audio decoder 24, and outputs the mixed result as a 5.1channel audio signal.

Next, referring to FIG. 2, the structure of the player application 150,which is executed by the CPU 11, is described.

The player application 150 includes a demultiplex (Demux) module, adecode control module, a sub-picture (Sub-Picture) decode module, asub-video (Sub-Video) decode module, a navigation (Navigation) decodemodule, a sub-audio (Sub-Audio) decode module, a graphics driver, anaudio driver, and a PCI stream transfer driver.

The Demux module is software that executes a demultiplex process forseparating, from the stream read out of the HD-DVD drive 18, main videodata, main audio data, graphics data (sub-picture data, sub-video dataand navigation data), and sub-audio data. The decode control module issoftware that controls decoding processes for the main video data, mainaudio data, graphics data (sub-picture data, sub-video data andnavigation data), and sub-audio data. The control of the decodingprocesses is executed on the basis of, e.g., reproduction controlinformation, which is multiplexed on the HD-DVD stream. The reproductioncontrol information is information for controlling a reproductionprocedure for the main video data and graphics data (sub-picture data,sub-video data and navigation data).

The sub-picture (Sub-Picture) decode module decodes the sub-picturedata. The sub-video (Sub-Video) decode module decodes the sub-videodata. The navigation (Navigation) decode module decodes the navigationdata. The sub-audio (Sub-Audio) module decodes the sub-audio data.

The graphics driver is software for controlling the GPU 120. The decodedsub-picture data, decoded sub-video data and decoded navigation are sentto the GPU 120 via the graphics driver. The graphics driver issuesvarious rendering instructions to the GPU 120.

The audio driver is software for controlling the audio codec 16. Thedecoded sub-audio data is sent to the audio codec 16 via the audiodriver.

The PCI stream transfer driver is software for transferring the streamvia the PCI bus 21. The main video data and main audio data aretransferred by the PCI stream transfer driver to the video decoder 25and audio decoder 24 via the PCI bus 21.

Next, referring to FIG. 3, a description is given of the functionalstructure of the software decoder that is realized by the playerapplication 150, which is executed by the CPU 11.

The software decoder, as shown in FIG. 3, includes a stream reading unit101, a decryption process unit 102, a demultiplex (Demux) unit 103, asub-picture decoder 104, a sub-video decoder 105, an advanced navigationdecoder 106, and a sub-audio decoder 107.

The stream (HD-DVD stream) that is stored on the HD-DVD media in theHD-DVD drive 18 is read out of the HD-DVD drive 18 by the stream readingunit 101. The HD-DVD stream is encrypted by, e.g., content scramblingsystem (CSS). The HD-DVD stream that is read out of the HD-DVD media bythe stream reading unit 101 is input to the decryption process unit 102.The decryption process unit 102 executes a process for decrypting theHD-DVD stream. The decrypted HD-DVD stream is input to the demultiplex(Demux) unit 103. The Demux 103 is realized by the Demux module in theplayer application 150. The Demux 103 separates, from the HD-DVD stream,main video data (MAIN VIDEO), main audio data (MAIN AUDIO), graphicsdata (Sub-Picture, Sub-Video and Advanced Navigation) and sub-audio data(Sub-Audio).

The main video data (MAIN VIDEO) is sent to the video decoder 25 via thePCI bus 21. The main video data (MAIN VIDEO) is decoded by the videodecoder 25. The decoded main video data has a resolution of 1920×1080pixels according to the HD standard, and is sent to the blending processunit 30 as a digital YUV video signal. The main audio data (MAIN AUDIO)is sent to the audio decoder 24 via the PCI bus 21. The main audio data(MAIN AUDIO) is decoded by the audio decoder 24. The decoded main audiodata (MAIN AUDIO) is sent to the audio mixer 31 as an I2S-format digitalaudio signal.

The sub-picture data, sub-video data and advanced navigation data aresent to the sub-picture decoder 104, sub-video decoder 105 and advancednavigation decoder 106. The sub-picture decoder 104, sub-video decoder105 and advanced navigation decoder 106 are realized by the sub-picture(Sub-Picture) decode module, sub-video (Sub-Video) decode module andnavigation (Navigation) decode module of the player application 150. Thesub-picture data, sub-video data and advanced navigation data, whichhave been decoded by the sub-picture decoder 104, sub-video decoder 105and advanced navigation decoder 106, are written in the VRAM 131. Thesub-picture data, sub-video data and advanced navigation data, whichhave been written in the VRAM 131, include RGB data and alpha data (A)in association with each pixel.

The sub-audio data is sent to the sub-audio decoder 107. The sub-audiodecoder 107 is realized by the sub-audio (Sub-audio) decode module ofthe player application 150. The sub-audio data is decoded by thesub-audio decoder 107. The decoded sub-audio data is converted to anI2S-format digital audio signal by the audio codec 16, and is sent tothe audio mixer 31.

The GPU 120 generates graphics data for forming a graphics screenpicture of 1920×1080 pixels, on the basis of the decoded results of thesub-picture decoder 104, sub-video decoder 105 and advanced navigationdecoder 106, that is, picture data corresponding to the sub-picturedata, sub-video data and advanced navigation data, which are written inthe VRAM 131 by the CPU 11. In this case, the three picture datacorresponding to the sub-picture data, sub-video data and advancednavigation data are blended by an alpha blending process that isexecuted by a mixer (MIX) unit 121 of the GPU 120.

In this alpha blending process, alpha data corresponding to the threepicture data written in the VRAM 131 are used. Specifically, each of thethree picture data written in the VRAM 131 contains RGB data and alphadata. The mixer (MIX) unit 121 executes the blending process on thebasis of the alpha data of the three picture data and positioninformation of each of the three picture data, which is told from theCPU 11. Thereby, the mixer (MIX) unit 121 generates a graphics screenpicture, which includes, for instance, the three picture data that areat least partly blended. As regards an area where the picture data areblended, new alpha data corresponding to the area is calculated by themixer (MIX) unit 121. The colors of the pixels in that area in thegraphics screen picture of 1920×1080 pixels, which includes no effectivepicture data, are black. The alpha value corresponding to the pixels inthe area, which includes no effective picture data, is a value (alpha=0)that indicates that these pixels are transparent.

In this way, the GPU 120 generates the graphics data (RGB) that form thegraphics screen picture of 1920×1080 pixels, and the alpha datacorresponding to the graphics data, on the basis of the decoded resultsof the sub-picture decoder 104, sub-video decoder 105 and advancednavigation decoder 106. As regards a scene in which only one of thepictures of the sub-picture data, sub-video data and advanced navigationdata, or the GPU 120 generates graphics data that corresponds to agraphics screen picture, in which the picture (e.g., 720×480) isdisposed on the surface of 1920×1080 pixels, and alpha datacorresponding to the graphics data.

The graphics data (RGB) and alpha data, which are generated by the GPU120, are sent as RGBA data to the blending process unit 30 via thegraphics bus 20.

Next, referring to FIG. 4, the blending process (alpha blending process)that is executed by the blending process unit 30 is explained.

The alpha blending process is a blending process in which graphics dataand main video data are blended on a pixel-by-pixel basis, on the basisof alpha data (A) that accompanies the graphics data (RGB). In thiscase, the graphics data (RGB) is used as an oversurface and is laid onthe video data. The resolution of the graphics data that is output fromthe GPU 120 is equal to that of the main video data that is output fromthe video decoder 25.

Assume now that main video data (Video) with a resolution of 1920×1080pixels was input to the blending process unit 30 as picture data C, andgraphics data with a resolution of 1920×1080 pixels was input to theblending process unit 30 as picture data G. In this case, on the basisof alpha data (A) with a resolution of 1920×1080 pixels, the blendingprocess unit 30 executes an arithmetic operation for overlaying thepicture data G on the picture data C in units of a pixel. Thisarithmetic operation is executed by the following equation (1):V=α×G+(1−α)C  (1)

where V is the color of each pixel of output picture data obtained bythe alpha blending process, and α is the alpha value corresponding toeach pixel of graphics data G.

Next, referring to FIG. 5, the blending process (alpha blendingprocess), which is executed by the MIX unit 121 of the GPU 120, isexplained.

Assume now that graphics data with a resolution of 1920×1080 pixels isgenerated from the sub-picture data and sub-video data that are writtenin the VRAM 131. Each of the sub-picture data and sub-video data has aresolution of, e.g., 720×480 pixels. In this case, each of thesub-picture data and sub-video data is accompanied with alpha data witha resolution of, e.g., 720×480 pixels.

For example, a picture corresponding to the sub-picture data is used asan oversurface, and a picture corresponding to the sub-video data isused as an undersurface.

The color of each pixel in an area where the picture corresponding tothe sub-picture data and the picture corresponding to the sub-video dataoverlap is given by the following equation (2):G=Go×αo+Gu(1−αo)  (2)

where G is the color of each pixel in the overlapping area, Go is thecolor of each pixel of the sub-picture data that is used as anoversurface, αo is the alpha value of each pixel of the sub-picture datathat is used as an oversurface, and Gu is the color of each pixel of thesub-video that is used as an undersurface.

The alpha value of each pixel in an area where the picture correspondingto the sub-picture data and the picture corresponding to the sub-videodata overlap is given by the following equation (3):α=αo+αu×(1−αo)  (3)

where α is the alpha value of each pixel in the overlapping area, and auis the alpha value of each pixel of the sub-video data that is used asan undersurface.

In this way, the MIX unit 121 of the GPU 120 blends the sub-picture dataand sub-video data by using that one of the alpha data corresponding tothe sub-picture data and the alpha data corresponding to the sub-videodata, which is to be used as the oversurface. Thereby, the MIX unit 121generates graphics data for forming a screen picture of 1920×1080pixels. Further, the MIX unit 121 of the GPU 120 calculates the alphavalue of each pixel of the graphics data for forming a screen picture of1920×1080 pixels, on the basis of the alpha data corresponding to thesub-picture data and the alpha data corresponding to the sub-video data.

Specifically, the MIX unit 121 of the GPU 120 executes the blendingprocess for blending a surface of 1920×1080 pixels (the color ofpixels=black, the alpha value of pixels=0), a surface of sub-video dataof 720×480 pixels, and a surface of sub-picture data of 720×480 pixels.Thereby, the MIX unit 121 calculates graphics data for forming a screenpicture of 1920×1080 pixels, and alpha data of 1920×1080 pixels. Thesurface of 1920×1080 pixels is used as a lowest surface, the surface ofthe sub-video data is used as a second lowest surface, and the surfaceof the sub-picture data is used as an uppermost surface.

In the screen picture of 1920×1080 pixels, the color of each pixel inthe area, where neither sub-picture data nor sub-video data is present,is black. The color of each pixel in the area, where only sub-picturedata is present, is the same as the normal color of each associatedpixel of the sub-picture data. Similarly, the color of each pixel in thearea, where only sub-video data is present, is the same as the normalcolor of each associated pixel of the sub-video data.

In the screen picture of 1920×1080 pixels, the alpha value correspondingto each pixel in the area, where neither sub-picture data nor sub-videodata is present, is zero. The alpha value of each pixel in the area,where only sub-picture data is present, is the same as the normal alphavalue of each associated pixel of the sub-picture data. Similarly, thealpha value of each pixel in the area, where only sub-video data ispresent, is the same as the normal alpha value of each associated pixelof the sub-video data.

FIG. 6 shows a state in which sub-video data of 720×480 pixels isoverlaid on main video data of 1920×1080 pixels.

In FIG. 6, graphics data is generated by a blending process that blendsa surface of 1920×1080 pixels (the color of pixels=black, the alphavalue of pixels=0) and a surface of sub-video data of 720×480 pixels ona pixel-by-pixel basis.

As has been described above, output picture data (Video+Graphics), whichis output to the display device, is generated by blending the graphicsdata and main video data.

In the graphics data of 1920×1080 pixels, the alpha value of each pixelin the area, where the sub-video data of 720×480 pixels is absent, iszero. Accordingly, the area where the sub-video data of 720×480 pixelsis absent is transparent. In this area, the main video data is displayedwith the degree of non-transparency of 100%.

Each pixel of the sub-video data of 720×480 pixels is displayed on themain video data with a degree of transparency that is designated by thealpha data corresponding to the sub-video data. For example, a pixel ofsub-video data with an alpha value=1 is displayed with 100%non-transparency, and a pixel of main video data corresponding to thispixel position is not displayed.

As is shown in FIG. 7, main video data, which is reduced to a resolutionof 720×480 pixels, can be displayed on a partial area of sub-video datathat is enlarged to a resolution of 1920×1080 pixels.

In one embodiment, the display mode illustrated in FIG. 7 is realizedusing a scaling function that is performed by the GPU 120 and a scalingfunction that is performed by the video decoder 25.

Specifically, in accordance with an instruction from the CPU 11, the GPU120 executes such a scaling process as to gradually increase theresolution (picture size) of sub-video data up to 1920×1080 pixels. Thisscaling process is executed using pixel interpolation. As the resolutionof the sub-video data becomes higher, the size of the area where thesub-video data of 720×480 pixels is not present (i.e. area with alphavalue=0) gradually decreases within the graphics data of 1920×1080pixels. Thereby, the size of the sub-video data, which is overlaid onthe main video data and displayed, gradually increases, while the sizeof the area with the alpha value=0 gradually decreases. If theresolution (picture size) of the sub-video data reaches 1920×1080pixels, the GPU 120 executes a blending process that overlays, on apixel-by-pixel basis, a surface of, e.g., 720×480 pixels (the color ofpixels=black, the alpha value of pixels=0) on the sub-video data of1920×1080 pixels. Thus, the area of 720×480 pixels with the alphavalue=0 is disposed on the sub-video data of 1920×1080 pixels.

On the other hand, in accordance with an instruction from the CPU 11,the video decoder 25 executes the scaling process that reduces theresolution of main video data to 720×480 pixels.

The main video data that is reduced to 720×480 pixels is displayed on anarea of 720×480 pixels with the alpha value=0, which is disposed on thesub-video data of 1920×1080 pixels. Specifically, the alpha data that isoutput from the GPU 120 can also be used as a mask for limiting the areawhere the main video data is to be displayed.

As stated above, the alpha data that is output from the GPU 120 canfreely be controlled by software. Thus, the graphics data caneffectively be overlaid on the main video data and displayed. Thereby,video expression with high interactivity can easily be realized.Furthermore, since the alpha data is automatically transferred alongwith the graphics data to the blending process unit 30 from the GPU 120,the software does not need to recognize the transfer of alpha data tothe blending process unit 30.

Next, referring to FIG. 8, a description is given of the operation fortransferring the main video data and graphics data to the blendingprocess unit 30.

The main video data is transferred as a digital YUV video signal fromthe video decoder 25 to the blending process unit 30. Depending on AVcontent that is included in an HD-DVD stream, there can be a case ofusing not HD (High Definition)-standard main video data but SD (StandardDefinition)-standard main video data. Thus, the video decoder 25 isconfigured to support both SD and HD. The number of vertical lines ofmain video data, which is output from the video decoder 25, is any oneof 480i, 480p, 1080i and 720p. In this case, 480i is the number ofvertical lines of an SD-standard interlace picture, 480p is the numberof vertical lines of an SD-standard progressive picture, 1080i is thenumber of vertical lines of an HD-standard interlace picture, and 720pis the number of vertical lines of an HD-standard progressive picture.

The GPU 120 outputs the alpha-data-added graphics data to the graphicsbus 20 as an RGBA-format digital video signal. The resolution of ascreen picture of the alpha-data-added graphics data is equal to that ofa screen picture of main video data. That is, under the control of theCPU 11, the GPU 120 outputs the alpha-data-added graphics data, whichcorresponds to any one of 480i, 480p, 1080i and 720p.

FIG. 9 illustrates a state in which alpha-data-added graphics data istransferred via the graphics bus 20.

The graphics bus 20 has a 32-bit width. As is shown in FIG. 9, graphicsdata (RGB=24 bits) and alpha data (A=8 bits) are transferred via thegraphics bus 20 in sync with a pixel clock signal. The pixel clocksignal is output from a pixel clock generator (PLL: Phase-Locked Loop),which is provided, for example, within the GPU 120. Symbols R1, G1, B1and A1 represent four components of red, green, blue and transparency(alpha) of a first pixel. Similarly, R2, G2, B2 and A2 represent fourcomponents of red, green, blue and transparency (alpha) of a secondpixel.

In this way, the graphics data (RGB) and alpha data (A) are sent to theblending process unit 30 in the state in which these data aresynchronized on a pixel-by-pixel basis. Thus, blending of graphics data(RGB) and main video data (YUV) can easily be executed without providingthe blending process unit 30 with a circuit for synchronizing thegraphics data (RGB) and alpha data (A).

It is not necessary to transfer the alpha data (A) and graphics data(RGB) via the same bus. As is shown in FIG. 10, it is possible totransfer the alpha data (A) and graphics data (RGB) via differenttransmission lines. In FIG. 10, the alpha data (A) is transferred fromthe GPU 120 to the blending process unit 30 via a first graphics bus20A, and the graphics data (RGB) is transferred from the GPU 120 to theblending process unit 30 via a second graphics bus 20B. The graphicsbuses 20A and 20B are provided between the GPU 120 and blending processunit 30.

Next, referring to FIG. 11, a first example of the structure of theblending process unit 30 is described.

The blending process unit 30, as shown in FIG. 11, includes a synccontrol unit 200, an RGBA-to-YUV conversion unit 201 and an α arithmeticunit 210.

The sync control unit 200 is a circuit for synchronizing a transferoperation for graphics data with alpha data (RGBA) by the GPU 120 with atransfer operation for main video data (YUV) by the video decoder 25 inunits of a screen (frame or field) on a pixel-by-pixel basis.

The GPU 120 operates in sync with a pixel clock signal (Pixel Clock) anda vertical sync signal (Vsync), and outputs graphics data with alphadata (RGBA) in sync with the pixel clock signal (Pixel Clock) andvertical sync signal (Vsync). Specifically, the GPU 120 begins to outputgraphics data with alpha data (RGBA), which corresponds to a first pixelof each screen, in sync with the vertical sync signal (Vsync), andsuccessively outputs graphics data with alpha data (RGBA), whichcorresponds to each of pixel groups in each screen, in sync with thepixel clock signal (Pixel Clock) The pixel clock signal is output from apixel clock generator (PLL: Phase-Locked Loop) 300. The pixel clocksignal is supplied to the GPU 120 and video decoder 25.

The vertical sync signal (Vsync) is output from a clock generator thatis provided within the GPU 120. This clock generator operates in syncwith the pixel clock signal. The GPU 120 outputs a vertical sync signal(Vsync) and a horizontal sync signal (Hsync) to the outside.

The sync control unit 200 delivers the vertical sync signal (Vsync) fromthe GPU 120 to the video decoder 25 so that the GPU 120 may function asa master and the video decoder 25 may function as a slave that operatesin sync with the vertical sync signal (Vsync) from the GPU 120.

Thereby, the video decoder 25 operates in sync with the same pixel clocksignal and vertical sync signal as the GPU 120, and outputs video data(YUV) in sync with the pixel clock signal and vertical sync signal.Specifically, the video decoder 25 begins to output video data (YUV),which corresponds to a first pixel of each screen, in sync with thevertical sync signal (Vsync) that has been received from the GPU 120,and successively outputs video data (YUV), which corresponds to each ofpixel groups in each screen, in sync with the pixel clock signal (PixelClock).

By feeding the vertical sync signal from the GPU 120 back to the GPU120, it becomes possible to synchronize a transfer operation forgraphics data with alpha data (RGBA) by the GPU 120 with a transferoperation for main video data (YUV) by the video decoder 25 in units ofa screen (frame or field) on a pixel-by-pixel basis. Therefore, withoutproviding a buffer circuit, for instance, within the blending processunit 30, it becomes possible to precisely blend the graphics data andvideo data on a pixel-by-pixel basis.

In a case where each of video data and graphics data is an interlacepicture, the sync control unit 200 generates, in sync with the verticalsync signal that is output from the GPU 120, a field identifier (FieldID) that identifies whether a screen image that is currently to beoutput is a top field or a bottom field, and delivers the generatedfield identifier (Field ID) to the video decoder 25. Interlace picturesignals are output in the order of a top field, a bottom field, a topfield, a bottom field, . . . . Thus, upon receiving the first verticalsync signal from the GPU 120, the sync control unit 200 generates afield identifier (Field ID=1) that is indicative of a top field.Subsequently, each time the sync control unit 200 receives a verticalsync signal from the GPU 120, the sync control unit 200 alternatelyoutputs a field identifier (Field ID=0) indicative of a bottom field anda field identifier (Field ID=1) indicative of a top field. Thereby, itbecomes possible to prevent occurrence of a field error between graphicsdata and video data.

The vertical sync signal from the GPU 120 may directly be input to thevideo decoder 25, without intervention of the sync control unit 200.

The RGBA-to-YUV conversion unit 201 converts the color space of thegraphics data (RGB) of the graphics data with alpha data (RGBA), whichis output from the GPU 120, from the RGB color space to the YUV colorspace, thereby generating graphics data with alpha data (YUVA) havingthe YUV color space. As the alpha data of the graphics data with alphadata (YUVA), the value that is added to the RGB data is used as such.The generated graphics data (YUVA) with alpha data is sent to the αarithmetic unit 210.

The α arithmetic unit 210 executes, on the YUV color space, anarithmetic operation (alpha blending arithmetic operation) for blendingthe graphics data (YUV) and video data (YUV) in units of a pixel, on thebasis of the alpha data (A) of the graphics data with alpha data (YUVA).Thereby, the α arithmetic unit 210 generates output picture data (YUV).

As has been described above, in the blending process unit 30 of thepresent embodiment, the alpha blending arithmetic operation is executednot on the RGB color space, but on the YUV color space. Thus, since nocolor conversion is performed for the main video data (YUV) that is usedas a main screen image, the real quality of HD-standard main video datais not degraded and a high-quality video output on which graphics datais overlaid can be obtained.

FIG. 12 shows a second example of the structure of the blending processunit 30.

In the structure shown in FIG. 12, the relationship between the masterand the slave in FIG. 11 is reversed. Specifically, the sync controlunit 200 delivers the vertical sync signal (Vsync) from the videodecoder 25 to the GPU 120 so that the video decoder 25 may function as amaster and the GPU 120 may function as a slave that operates in syncwith the vertical sync signal (Vsync) from the video decoder 25.Thereby, the GPU 120 operates in sync with the same pixel clock signaland vertical sync signal as the video decoder 25, and outputs graphicsdata with alpha data (RGBA) in sync with the pixel clock signal andvertical sync signal.

The vertical sync signal from the video decoder 25 may directly be inputto the GPU 120, without intervention of the sync control unit 200.

FIG. 13 shows a third example of the structure of the blending processunit 30.

The blending process unit 30 shown in FIG. 13 does not include the synccontrol unit 200. Instead of the sync control unit 200, a vertical syncsignal generator 400, which is common to the video decoder 25 and GPU120, is provided. Thereby, each of the video decoder 25 and GPU 120operates in sync with a vertical sync signal that is output from thevertical sync signal generator 400 and a pixel clock signal that isoutput from the PLL 300. It is thus possible to synchronize a transferoperation for graphics data with alpha data (RGBA) with a transferoperation for main video data (YUV) in units of a screen (frame orfield) on a pixel-by-pixel basis.

FIG. 14 shows a fourth example of the structure of the blending processunit 30.

In the blending process unit 30 shown in FIG. 14, a YUV-to-RGBconversion unit 205 and selectors 206 and 207 are provided in additionto the structure of the blending process unit 30 shown in FIG. 11.

The YUV-to-RGB conversion unit 205 converts the color space of mainvideo data from the YUV color space to the RGB color space, andgenerates main video data of the RGB color space.

The selector 206 selects one of an input port and an output port of theYUV-to-RGB conversion unit 205, and connects the selected port to the αarithmetic unit 210. In the case where the selector 206 selects theoutput port of the YUV-to-RGB conversion unit 205, main video data ofthe RGB color space is supplied to the α arithmetic unit 210. On theother hand, in the case where the selector 206 selects the input port ofthe YUV-to-RGB conversion unit 205, main video data of the YUV colorspace bypasses the YUV-to-RGB conversion unit 205 and goes to the αarithmetic unit 210.

The selector 207 selects one of an input port and an output port of theRGBA-to-YUV conversion unit 201, and connects the selected port to the αarithmetic unit 210. In the case where the selector 207 selects theoutput port of the RGBA-to-YUV conversion unit 201, graphics data withalpha data (YUVA) of the YUV color space is supplied to the α arithmeticunit 210. On the other hand, if the selector 207 selects the input portof the RGBA-to-YUV conversion unit 201, graphics data with alpha data(RGBA) of the RGB color space bypasses the RGBA-to-YUV conversion unit201 and goes to the α arithmetic unit 210.

The selection operations of the selectors 206 and 207 are commonlycontrolled by a switch signal SW1. The switch signal SW1 is generated,for example, from a control register that is provided in the southbridge 14, in which color conversion mode designation information iswritten by the CPU 11. The color conversion mode designation informationdesignates one of a YUV blend mode for executing a blending process onthe YUV color space and an RGB blend mode for executing a blendingprocess on the RGB color space.

In the YUV blend mode, the selector 206 selects the input port of theYUV-to-RGB conversion unit 205, and the selector 207 selects the outputport of the RGBA-to-YUV conversion unit 201. Thereby, graphics data andmain video data are blended on the YUV space.

In the RGB blend mode, the selector 206 selects the output port of theYUV-to-RGB conversion unit 205, and the selector 207 selects the inputport of the RGBA-to-YUV conversion unit 201. Thereby, graphics data andmain video data are blended on the RGB space.

The selection of the YUV blend mode/RGB blend mode can be executed inaccordance with color conversion mode control information that ismultiplexed in an HD-DVD stream. The color conversion mode controlinformation is set, for example, on a scene-by-scene basis. The CPU 11interprets the color conversion mode control information and instructsthe YUV blend mode or RGB blend mode to the blending process unit 30.For example, the YUV blend mode is used in normal cases, and the YUVblend mode is switched to the RGB blend mode when the display mode ischanged to the mode as illustrated in FIG. 7. As has been describedabove, by effecting dynamic switching between the YUV blend mode and theRGB blend mode, the blending process can be executed in the mode that issuited to a scene to be reproduced.

A GUI or an operation switch that enables the user to designate the YUVblend mode/RGB blend mode may be provided. Thereby, in accordance withthe user's operation, the YUV blend mode/RGB blend mode switching may beforcibly executed. It is thus possible to obtain an output picture withan image quality that satisfies the taste of the user.

FIG. 15 shows arithmetic formulae for converting the RGB color space tothe YUV color space, and arithmetic formulae for alpha blending that isexecuted on the YUV color space.

In the alpha blending on the YUV color space, too, the alpha data (A)that accompanies the graphics data of the RGB color space can be used assuch.

FIG. 16 shows a fifth example of the structure of the blending processunit 30.

Video data that is output from the video decoder 25 is 4:2:2 format datain which a resolution of a chrominance signal is lower than a resolutionof a luminance signal. On the other hand, graphics data that is outputfrom the GPU 120 is RGB data. If the color space of the graphics data isconverted from RGB color space to the YUV color space, the graphics databecomes 4:4:4 format YUV data in which the resolution of a luminancesignal is equal to the resolution of a chrominance signal.

In order to obtain a high-quality output picture in which graphics dataand video data are blended, the blending process unit 30 includes a4:2:2-to-4:4:4 conversion unit 204. The 4:2:2-to-4:4:4 conversion unit204 up-samples the YUV 4:2:2 format video data, and generates YUV 4:4:4format video data. The YUV 4:4:4 format video data is sent to the αarithmetic unit 210.

Based on alpha data (A) of the graphics data with alpha data (YUVA),which is output from the RGBA-to-YUV conversion unit 201, the αarithmetic unit 210 executes an arithmetic operation (alpha blendingarithmetic operation) for blending the graphics data (YUV 4:4:4) andvideo data (YUV 4:4:4) on a pixel-by-pixel basis, thereby generating YUV4:4:4 format output picture data.

In the blending process unit 30, as described above, the video data isup-sampled so as to conform to the picture format of the graphics data,and then blended with the graphics data. Thereby, a high-quality outputpicture can be obtained.

FIG. 17 shows a sixth example of the structure of the blending processunit 30.

In the blending process unit 30 shown in FIG. 17, a 4:4:4-to-4:2:2conversion unit 202 and selectors 208 and 209 are provided in additionto the structure of the blending process unit 30 shown in FIG. 16.

The 4:4:4-to-4:2:2 conversion unit 202 down-samples 4:4:4 formatgraphics data with alpha data (YUVA), which has been converted to theYUV color space by the RGBA-to-YUV conversion unit 201, therebygenerating 4:2:2 format graphics data with alpha data (YUVA). In thiscase, the alpha data is not down-sampled and the alpha data has the sameresolution as the luminance signal Y.

The selector 208 selects one of an input port and an output port of the4:2:2-to-4:4:4 conversion unit 204, and connects the selected port tothe α arithmetic unit 210. In the case where the selector 208 selectsthe output port of the 4:2:2-to-4:4:4 conversion unit 204, YUV 4:4:4format main video data is supplied to the α arithmetic unit 210. On theother hand, if the selector 208 selects the input port of the4:2:2-to-4:4:4 conversion unit 204, YUV 4:2:2 format main video databypasses the 4:2:2-to-4:4:4 conversion unit 204 and goes to the αarithmetic unit 210.

The selector 209 selects one of an input port and an output port of the4:4:4-to-4:2:2 conversion unit 202, and connects the selected port tothe α arithmetic unit 210. In the case where the selector 209 selectsthe output port of the 4:4:4-to-4:2:2 conversion unit 202, YUV 4:2:2format graphics data with alpha data is supplied to the α arithmeticunit 210. On the other hand, if the selector 209 selects the input portof the 4:4:4-to-4:2:2 conversion unit 202, YUV 4:4:4 format graphicsdata with alpha data bypasses the 4:4:4-to-4:2:2 conversion unit 202 andgoes to the α arithmetic unit 210.

The selection operations of the selectors 208 and 209 are commonlycontrolled by a switch signal SW2. The switch signal SW2 is generated,for example, from a control register that is provided in the southbridge 14, in which color conversion mode designation information iswritten by the CPU 11. The color conversion mode designation informationdesignates one of a 4:4:4 blend mode for blending YUV 4:4:4 formatpictures and a 4:2:2 blend mode for blending YUV 4:2:2 format pictures.

In the 4:4:4 blend mode, the selector 208 selects the output port of the4:2:2-to-4:4:4 conversion unit 204, and the selector 209 selects theinput port of the 4:4:4-to-4:2:2 conversion unit 202. Thereby, YUV 4:4:4format main video data and YUV 4:4:4 format graphics data are blended bythe α arithmetic unit 210.

In the 4:2:2 blend mode, the selector 208 selects the input port of the4:2:2-to-4:4:4 conversion unit 204, and the selector 209 selects theoutput port of the 4:4:4-to-4:2:2 conversion unit 202. Thereby, YUV4:2:2 format main video data and YUV 4:2:2 format graphics data areblended by the α arithmetic unit 210.

The switching between the 4:4:4 blend mode and 4:2:2 blend mode canforcibly be effected by the user's operation of a GUI or an operationswitch. YUV 4:2:2 format video signals are supported by many AVapparatuses, and have a high flexibility in application uses. On theother hand, YUV 4:4:4 format video signals have a higher quality thanYUV 4:2:2 format video signals, but the types of AV apparatuses thatsupport the YUV 4:4:4 format video signals are limited. Thus, byproviding the function of switching between the 4:4:4 blend mode and4:2:2 blend mode, it becomes possible to meet both the requirements forflexibility in use and image quality. The function of switching betweenthe 4:4:4 blend mode and 4:2:2 blend mode may be used in combinationwith the function of switching between the YUV blend mode and RGB blendmode. In this case, only when the YUV blend mode is selected, can theswitching between the 4:4:4 blend mode and 4:2:2 blend mode be executed.

The circuits for synchronization, which have been described withreference to FIG. 11 to FIG. 13, are also applicable to the structuresshown in FIG. 16 and FIG. 17.

FIG. 18 shows a seventh example of the structure of the blending processunit 30.

In the blending process unit 30 shown in FIG. 18, a 4:4:4-to-4:2:2conversion unit 211 is provided in addition to the sync control unit 200and RGB-to-YUV conversion unit 201, which are shown in FIG. 11, and inaddition to the 4:2:2-to-4:4:4 conversion unit 204, which is shown inFIG. 16.

Graphics data with alpha data (RGBA) from the GPU 120 is delivered tothe RGBA-to-YUV conversion unit 201. The RGBA-to-YUV conversion unit 201converts the color space of the graphics data (RGB) from the RGB colorspace to the YUV color space, thereby generating graphics data withalpha data (YUVA) having the YUV 4:4:4 format. As the alpha data, thevalue that is added to the RGB data is used as such. The generatedgraphics data (YUVA) is sent to the α arithmetic unit 210.

YUV 4:2:2 format video data from the video decoder 25 is delivered tothe 4:2:2-to-4:4:4 conversion unit 204. The 4:2:2-to-4:4:4 conversionunit 204 up-samples the YUV 4:2:2 format video data, and generates YUV4:4:4 format video data. The YUV 4:4:4 format video data is sent to theα arithmetic unit 210.

Based on alpha data (A) of the graphics data with alpha data (YUVA), theα arithmetic unit 210 executes an arithmetic operation (alpha blendingarithmetic operation) for blending the graphics data (YUV 4:4:4) andvideo data (YUV 4:4:4) on a pixel-by-pixel basis, thereby generating YUV4:4:4 format output picture data. The YUV 4:4:4 format output picturedata is directly sent to the video encoder 40, or is down-sampled to aYUV 4:2:2 format in the 4:4:4-to-4:2:2 conversion unit 211 and then sentto the video encoder 40.

As has been described above, in the blending process unit 30, 4:4:4format pictures are subjected to the blending process, and the obtainedoutput picture is converted to the 4:2:2 format and is output. Thereby,a high-quality blended output picture is obtained, and the flexibilityin application uses is enhanced.

According to the HD-DVD player of the present embodiment, the transferoperation for graphics data with alpha data (RGBA) by the GPU 120 can besynchronized with the transfer operation for main video data (YUV) bythe video decoder 25 in units of a screen (frame or field) on apixel-by-pixel basis. Therefore, blending of graphics data and videodata can be executed with high precision in units of a pixel, withoutthe need to provide a buffer circuit or the like in the blending processunit 30.

As has been described above in detail, the present invention makes itpossible to precisely execute blending between video data and graphicsdata with a simple configuration.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A reproducing apparatus comprising: a graphics processing unit thatoutputs graphics data that comprises first video data, which forms afirst screen image, in sync with a vertical sync signal and a pixelclock signal; a video decoder that outputs second video data, whichforms a second screen image, in sync with the vertical sync signal andthe pixel clock signal; a blending process unit that executes, on apixel-by-pixel basis, a blending process for blending the graphics data,which is output from the graphics processing unit, and the second videodata, which is output from the video decoder, wherein each pixel of thesecond video data is inputted to the blending process unitsimultaneously with a corresponding pixel of the graphics data basedupon the pixel clock signal and the vertical sync signal; and a picturedata output unit that outputs picture data, which is obtained by theblending process, to a display apparatus.
 2. The reproducing apparatusaccording to claim 1, wherein the first screen image has the sameresolution as the second screen image.
 3. The reproducing apparatusaccording to claim 1, wherein the blending process unit executes anarithmetic operation for blending the graphics data and the second videodata.
 4. The reproducing apparatus according to claim 1, wherein theblending process unit executes an arithmetic operation for overlayingthe graphics data on the second video data, on the basis of alpha datathat indicates a degree of transparency of each of pixels of thegraphics data.
 5. The reproducing apparatus according to claim 1,wherein: one of the graphics processing unit and the video decoderfunctions as a master, and the other of the graphics processing unit andthe video decoder functions as a slave; and the slave receives thevertical sync signal, which is output from the master, and operates insync with the pixel clock signal and the vertical sync signal that isreceived from the master.
 6. The reproducing apparatus according toclaim 1, further comprising a clock generator that generates a clocksignal, wherein the graphics processing unit and the video decoderreceive the clock signal from the clock generator as the pixel clocksignal.
 7. The reproducing apparatus according to claim 1, furthercomprising a vertical sync signal generator that generates the verticalsync signal, wherein the graphics processing unit and the video decoderreceive the vertical sync signal from the vertical sync signalgenerator.
 8. The reproducing apparatus according to claim 1, wherein:each of the graphics data and the second video data is an interlacepicture; the vertical sync signal is output from one of the videodecoder and the graphics processing unit; and the reproducing apparatusfurther comprises a control unit that generates a field identifier,which identifies whether a screen image that is currently to be outputis a top field or a bottom field, in sync with the vertical sync signalthat is output from said one of the video decoder and the graphicsprocessing unit, and supplies the generated field identifier to theother of the video decoder and the graphics processing unit.
 9. Thereproducing apparatus according to claim 1, wherein the graphicsprocessing unit generates the graphics data by combining, on apixel-by-pixel basis, first picture data and second picture data, whichare stored in a memory.
 10. A reproducing apparatus comprising: aseparation unit that separates compression-encoded graphics data, whichcomprises compression-encoded first video data, and compression-encodedsecond video data from a motion picture stream which is read out of astorage medium; a first decoding unit that decodes the separatedcompression-encoded graphics data; a graphics data output unit thatgenerates displayable graphics data, which forms a first screen imagecomprising the first video data, on the basis of a decoded result of thefirst decoding unit, and outputs the generated displayable graphics datain sync with a vertical sync signal and a pixel clock signal; a seconddecoding unit that decodes the separated compression-encoded secondvideo data, generates displayable second video data that forms a secondscreen image, and outputs the generated displayable video data in syncwith the vertical sync signal and the pixel clock signal; a blendingprocess unit that executes, on a pixel-by-pixel basis, a blendingprocess for blending the displayable graphics data that is output fromthe graphics data output unit and the displayable second video data thatis output from the second decoding unit, wherein each pixel of thedisplayable second video data is inputted to the blending process unitsimultaneously with a corresponding pixel of the displayable graphicsdata based upon the pixel clock signal and the vertical sync signal; anda picture data output unit that outputs blended picture data, which isobtained by the blending process unit, to a display apparatus.
 11. Anaudiovisual data reproducing apparatus comprising: an optical disc driveconfigured to read audiovisual data from an optical disc, theaudiovisual data comprising graphics data, which comprises first videodata, and second video data; a graphics processing unit that outputs thegraphics data, which forms a first screen image, in sync with a verticalsync signal and a pixel clock signal; a video decoder that outputs thesecond video data, which forms a second screen image, in sync with thevertical sync signal and the pixel clock signal; a blending process unitthat executes, on a pixel-by-pixel basis, a blending process forblending the graphics data, which is output from the graphics processingunit, and the second video data, which is output from the video decoder,wherein each pixel of the second video data is inputted to the blendingprocess unit simultaneously with a corresponding pixel of the graphicsdata based upon the pixel clock signal and the vertical sync signal; anda picture data output unit that outputs picture data, which is obtainedby the blending process unit, to a display apparatus.
 12. Thereproducing apparatus according to claim 11, wherein the first screenimage has the same resolution as the second screen image.
 13. Thereproducing apparatus according to claim 11, wherein the blendingprocess unit executes an arithmetic operation for blending the graphicsdata and the second video data.
 14. The reproducing apparatus accordingto claim 11, wherein the blending process unit executes an arithmeticoperation for overlaying the graphics data on the second video data, onthe basis of alpha data that indicates a degree of transparency of eachof pixels of the graphics data.
 15. The reproducing apparatus accordingto claim 11, wherein: one of the graphics processing unit and the videodecoder functions as a master, and the other of the graphics processingunit and the video decoder functions as a slave; and the slave receivesthe vertical sync signal, which is output from the master, and operatesin sync with the pixel clock signal and the vertical sync signal that isreceived from the master.
 16. The reproducing apparatus according toclaim 11, further comprising a clock generator that generates a clocksignal, wherein the graphics processing unit and the video decoderreceive the clock signal from the clock generator as the pixel clocksignal.
 17. The reproducing apparatus according to claim 11, furthercomprising a vertical sync signal generator that generates the verticalsync signal, wherein the graphics processing unit and the video decoderreceive the vertical sync signal from the vertical sync signalgenerator.
 18. The reproducing apparatus according to claim 11, wherein:each of the graphics data and the second video data is an interlacepicture; the vertical sync signal is output from one of the videodecoder and the graphics processing unit; and the reproducing apparatusfurther comprises a control unit that generates a field identifier,which identifies whether a screen image that is currently to be outputis a top field or a bottom field, in sync with the vertical sync signalthat is output from said one of the video decoder and the graphicsprocessing unit, and supplies the generated field identifier to theother of the video decoder and the graphics processing unit.
 19. Thereproducing apparatus according to claim 11, wherein the graphicsprocessing unit generates the graphics data by combining, on apixel-by-pixel basis, first picture data and second picture data, whichare stored in a memory.